Monomeric 16-Electron π-Diborene Complexes of Zn(II) and Cd(II).

Despite the prevalence of stable π-complexes of most d10 metals, such as Cu(I) and Ni(0), with ethylene and other olefins, complexation of d10 Zn(II) to simple olefins is too weak to form isolable complexes due to the metal ion's limited capacity for π-backdonation. By employing more strongly donating π-ligands, namely neutral diborenes with a high-lying π(B═B) orbital, monomeric 16-electron M(II)-diborene (M = Zn, Cd) π-complexes were synthesized in good yields. Metal-B2 π-interactions in both the solid and solution state were confirmed by single-crystal X-ray analyses and their solution NMR and UV-vis absorption spectroscopy, respectively. The M(II) centers adopt a trigonal planar geometry and interact almost symmetrically with both boron atoms. The MB2 planes significantly twist out of the MX2 planes about the M-centroid(B-B) vector, with angles ranging from 47.0° to 85.5°, depending on the steric interactions between the diborene ligand and the MX2 fragment.